There are numerous potential applications of carbon nanotubes (CNTs) because of their unique mechanical, physical, electrical, chemical and biological properties. For example, ultra low resistance conductors, semiconductors, highly efficient electron emitters, ultra-strong lightweight fibers for structural applications, lasers, and gas sensors can all be manufactured by using CNTs. For reviews of CNT technology, properties and applications, see Baughman et al., “Carbon Nanotubes—the Route Toward Applications”, Science, volume 297, pages 787-792 (2002); Michael J. O'Connell (Editor) “Carbon Nanotubes—Properties and Applications”, CRC Taylor & Francis, New York (2006); Yury Gogotsi (Editor) “Nanomaterials Handbook”, CRC Taylor & Francis, New York (2006).
Pure multi-wall or single-wall CNTs may be used to replace oxides such as indium tin oxide (ITO) in production of electrically conductive transparent coatings deposited on electrically insulating transparent substrates. For example, see Gruner, “Carbon Nanotube Films for Transparent and Plastic Electronics”, J. Mater. Chem., volume 16, pages 3533-3539 (2006); Wu et al., “Transparent Conductive Carbon Nanotube Films”, Science, volume 305, pages 1273-1276 (2004); Schmidt et al., “The Effect of Aggregation on the Electrical conductivity of Spin-Coated Polymer/Carbon Nanotube Composite Films”, Langmuir, volume 23, pages 5707-5712 (2007); Gruner, “Carbon Nanonets Spark New Electronics”, Scientific American, pages 76-83, May (2007); Zhongrui et al., “Does the Wall Number of Carbon Nanotubes Matter as Conductive Transparent Material?”, Appl. Phys. Lett., volume 91, pages 053115-1-053115-3 (2007); Glatkowski et al., “Coatings Comprising Carbon Nanotubes and Methods for Forming Same”, U.S. Pat. No. 7,060,241; Arthur et al. “Method for Patterning Carbon Nanotube Coating and Carbon Nanotube Wiring”, U.S. Patent Application Publication No. 2004/0099438; and Rinzler et al., “Transparent Electrodes from Single Wall Carbon Nanotubes”, U.S. Patent Application Publication No. 2004/0197546A1.
A variety of synthesis techniques for preparing CNTs exist. These techniques include for example carbon arc, laser ablation, chemical vapor deposition, high pressure carbon monoxide process (HiPco), and cobalt-molybdenum catalyst process (CoMoCat). These techniques yield products that comprise a mixture of metallic and semiconducting CNTs. Depending on the preparation method, the semiconducting component of this mixture may easily be higher than 65%, which may severely limit the application of these materials in preparation of electrically conductive transparent coatings.
In a publication entitled “Titanium Monomers and Wires Adsorbed on Carbon Nanotubes: A First Principles Study”, Nanotechnology, volume 17, pages 1154-1159 (2006), Fagan et al. describe a theoretical study of Ti monomers and wires interacting with a semiconductor single-wall carbon nanotube, by inside as well as outside faces. Fagan et al. only provide a theoretical study without actual data.
In sum, there exists a need for new or improved electrically conductive transparent coatings and methods of making these materials.